3,Standard pleated primary filter, gradient-type structure to
provide maximum airflow filter area, which is five times of the
plane-type filter, welded steel protect net using surface rust
treatment, can be well fixed linear pleated structure, protect
filter media not punctured and prevent media not deformed due to
excessive pressure, to ensure that filter surface is fully
utilized. Can be common or moisture-proof paper frame, recycled or
incinerated after use, non-pollution, environmental compliance.